The present invention relates to shaft seal structures of vacuum pumps that draw gas by operating a gas conveying body in a pump chamber through rotation of a rotary shaft.
Japanese Laid-open Patent Publication Nos. 60-145475, 2-157490, 3-89080, 6-101674 describe a vacuum pump that includes a plurality of rotors. Each rotor functions as a gas conveying body. Two rotors rotate as engaged with each other, thus conveying gas through a pump chamber. More specifically, one rotor is connected to a first rotary shaft and the other is connected to a second rotary shaft. A motor drives the first rotary shaft. A gear mechanism transmits the rotation of the first rotary shaft to the second rotary shaft.
The gear mechanism is located in an oil chamber that retains lubricant oil. The pump of Japanese Laid-open Patent Publication No. 60-145475 uses a labyrinth seal that seals the space between the oil chamber and the pump chamber to prevent the lubricant oil from leaking from the oil chamber to the pump chamber. More specifically, a partition separates the oil chamber from the pump chamber and has a through hole through which a rotary shaft extends. The labyrinth seal is fitted between the wall of the through hole and the corresponding portion of the rotary shaft. The pump of Japanese Laid-open Patent Publication No. 2-157490 employs a lip seal that seals the space between an oil chamber and a pump chamber. The pump of Japanese Laid-open Patent Publication No. 3-89080 includes a bearing chamber for accommodating a bearing that supports a rotary shaft. An intermediate chamber is formed between the bearing chamber and the pump chamber. A partition separates the bearing chamber from the intermediate chamber and has a through hole through which a rotary shaft extends. A labyrinth seal is fitted between the wall of the through hole and the rotary shaft. The pump of Japanese Laid-open Patent Publication No. 6-101674 includes a lip seal and a labyrinth seal. The seals are fitted between the wall of a through hole of a partition that separates the oil chamber from the pump chamber and a rotary shaft that extends through the through hole.
However, it is difficult to reliably stop an oil leak only with a lip seal or a labyrinth seal. For example, in the pump of Japanese Laid-open Publication No. 6-101674, which uses the lip seal and the labyrinth seal, if the life of the lip seal comes to an end, the oil leak must be stopped only by the labyrinth seal. The stopping of the oil leak thus becomes less reliable.
Accordingly, it is an objective of the present invention to improve an effect of a vacuum pump of preventing oil from leaking to a pump chamber.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the present invention provides a vacuum pump that draws gas by operating a gas conveying body in a pump chamber through rotation of a rotary shaft. The vacuum pump includes an oil housing member, which forms an oil zone adjacent to the pump chamber. The rotary shaft has a projecting section that projects from the pump chamber to the oil zone through the oil housing member. An annular shaft seal is located around the projecting section to rotate integrally with the rotary shaft. The shaft seal has a first seal forming surface that opposes the oil housing member. A second seal forming surface is formed on the oil housing member. The second seal forming surface opposes the first seal forming surface. A pumping means is formed at the first seal forming surface. The pumping means urges oil between the first and second seal forming surfaces to move from a side corresponding to the pump chamber toward the oil zone when the rotary shaft rotates.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.